Objective: To study the development of lymphatic vessels after keratoplasty and to explore the molecular mechanisms of corneal lymphangiogenesis in transplanted corneas.
Methods: Experimental research. The development of corneal lymphangiogenesis was examined by LYVE-1 immunohistochemistry and whole mount immunofluorescence 1, 3, 7, 10, 14, 30 and 60 days after corneal transplantation, then lymphatic vessels counting (LVC)was evaluated. The expression of vascular endothelial growth factor-C (VEGF-C) in transplanted corneas was examined by immunohistochemistry, enzyme-linked immunosorbent assay (ELISA), and real time-PCR at same time. In addition, the inflammatory index (IF) was recorded at each time point. The association of VEGF-C and IF with LVC in transplanted corneas was examined. Analysis of the significance of differences between two groups was performed using paired Student's t-test. Pearson's analysis was used to analyze the correlation between VEGF-C, IF and LVC.
Results: Corneal lymphangiogenesis occurred in the stroma with LVC (1.8 ± 0.3) on Day 3, then developed and reached the peak with LVC (9.1 ± 1.5) on Day 14 after corneal transplantation. Both VEGF-C protein and mRNA up-regulated dramatically in rat transplanted corneas. The immunoreactivity reached the peak on the 3(rd) day and the 14(th) day after keratoplasty. Compared with the expression of VEGF-C mRNA (1.62 ± 0.08 copies/g) on Day 3, the expression of VEGF-C mRNA (2.48 ± 0.03 copies/g) significantly increased 14 days after the transplantation (t = 4.296, P = 0.02). LVC was strongly and positively correlated with IF (r = 0.55, P = 0.003) and the expression of VEGF-C mRNA (r = 0.51, P = 0.003).
Conclusions: Corneal lymphangiogenesis correlates closely with corneal inflammation. The increased expression of VEGF-C in the cornea may be one of the important molecular mechanisms in the occurrence of corneal lymphangiogenesis after keratoplasty.